An IDE multiplexer based on 8255 PIO. It's construction is
very simple, however reading in MODE 1 givies 19T Z80 per byte.
The 8255 is seen in ports #1B, #3B, #5B, #7B and only one
logic chip is behind 8255 outputs. Also, the 8255 inside MB-02
can be used with special cable (no changes inside required).
If the power supply for disk is separated from power supply for IDE8255, the /ATCS0, /ATCS1, /ATRD and /ATWR lines behave as being in low state, when the IDE8255 is off. This can result in buring the disk. (We buried this way the CL-SH260-15QC-D chip of Seagate ST351A/X.)
To prevent such situation, the /ATCS0 should not be connected directly to GND, but with transistor (as OC with +5V on base). The /ATCS1 instead of being connected directly to +5V, should be separated with 1N4148 diode. The changes are not required, when there is only one power switch for both IDE8255 and disk.
Amstrad CPC version
A special version of IDE8255 was prepared for Amstrad CPC. The 8255 is seen in following ports:
|PA||#F8E6, #FAE6, #FCE6, #FEE6|
|PB||#F9E6, #FBE6, #FDE6, #FFE6|
|PC||#F8E7, #FAE7, #FCE7, #FEE7|
|RS||#F9E7, #FBE7, #FDE7, #FFE7|
As while reading data the PA and PB are read periodicly, eight INI comannecs can be used in a row, reading following ports: #F8E6, #F9E6, #FAE6, #FBE6, #FCE6, #FDE6, #FEE6, #FFE6. Of course this can be done only with e.g. #F8E6 and #F9E6, but this requires more frequent reloading of B register (of Z80CPU).
Files for download
- ide8255-003.zip 44.0kB (2004-02-13 17:07)
- Board v003, Eagle data files.
- ide8255.txt 4.5kB (2003-09-18 15:19)
- [en] The idea of fast IDE multiplexer based on 8255.
Links to other pages
- PL3MEM - ZX Spectrum IDE (ATA)
- External box for ZX Spectrum with 128kB EPROM, 32kB SRAM in ZX+3 switching and 16b IDE interface.
- Two YABUS slots for ZX Spectrum computers.
- 4MB RAM extension for Timex FDD 3 with YABUS support.
- Low level floppy and hard disk drivers for Z80.
- PPI 8255 parallel interface
- Most popular parallel interfaces based on 8255 PPI. Hardware type, port addresses, slot type, description of options.